The present invention relates to a process for forming a photoresist pattern in the manufacture of a semiconductor device. More particularly, it relates to a process for forming a fine photoresist pattern which improves the resistance of the pattern to the xe2x80x9cpost exposure delay effectxe2x80x9d by controlling the temperature of the photoresist composition while it is coated on the semiconductor substrate.
In the photolithography process for forming semiconductor devices, resolution depends upon the wavelength of the light sourcexe2x80x94the shorter the wavelength, the more minute the pattern that can be formed.
Recently, chemical amplification-type photoresists for use with deep ultra-violet light sources (xe2x80x9cDUV photoresistsxe2x80x9d) have been investigated in order to achieve high sensitivity in the minute image-formation processes used in photolithography processes for preparing semiconductor devices. Such photoresists are prepared by blending a photoacid generator and matrix resin polymer having an acid labile group to form a photoresist composition which is coated on a substrate, for example a silicon wafer.
According to the reaction mechanism of such a photoresist, the photoacid generator generates acid when it is illuminated by a light source, and the main chain or branched chain of the resin reacts with the generated acid to be decomposed or crosslinked. The polarity change of the resin induces solubility differences between the exposed portion and unexposed portion in the developing solution, to form a predetermined pattern.
In general, an acceptable photoresist (sometimes abbreviated herein as xe2x80x9cPRxe2x80x9d) must satisfy various requirements such as excellent etching resistance, heat resistance and adhesiveness, and more preferably, it should have the ability to be developed in a 2.38 wt % aqueous tetramethylammonium hydroxide (TMAH) solution. However, it is very difficult to synthesize a polymer that satisfies all of these requirements. For example, a polymer having a polyacrylate main chain can be easily synthesized, but it has poor etching resistance and has difficulties in the developing process. In order to secure etching resistance, it has been considered to add an alicyclic unit to the main chain of the PR polymer. However, in this case, another practical problem occurs in the process for manufacturing the semiconductor. That is, the acid generated by exposure of the photoresist may react with environmental amine compounds and thereby be reduced during the time between exposure and post exposure baking (xe2x80x9cpost exposure delay effectxe2x80x9d). Thus, the resultant pattern may be deformed or the formed pattern may have a T-shape (i.e., xe2x80x9cT-toppingxe2x80x9d of the pattern). The concentration of amine must be minimized in the manufacturing environment because these phenomena become more serious when the concentration of environmental amine is more than 30ppb.
Some methods to overcome these phenomena have been described in the prior art; for example, (1) adding amine to the PR composition, (2) adding a xe2x80x9csweetxe2x80x9d photoacid generator to the PR composition (See Frank Houlihan et al., Journal of Photopolymer Science and Technology, Vol. 11, No. 3, 1998, 419-430), and (3) improving the PR resin itself (See J. Byers et al., Journal of Photopolymer Science and Technology, Vol. 11, No. 3, 1998, 465-474). However, these methods require additional processes to control the concentration of amine in the environment, because they are only effective when the concentration of environmental amine is less than 5ppb, thereby resulting in a high manufacturing cost.
An object of the present invention is to overcome the disadvantages described above, and to provide a process for forming a fine photoresist pattern in the manufacture of semiconductor devices. The process of the present invention improves the resistance of the photoresist pattern to post exposure delay effect by controlling the temperature of the photoresist composition while it is being coated on the semiconductor substrate.